The present invention relates generally to DC-DC power converters. More particularly, this invention pertains to DC-DC converters optimized for high voltage applications.
Large data centers can host thousands of servers consuming significant energy. Conventionally, energy in such data centers has been distributed by single or three-phase AC voltages. To minimize the number of power conversion stages and to make it easier to attach more renewable energy sources to improve the overall energy efficiency of such data centers, power is distributed via a high voltage DC bus within the data center. Such high voltage is normally around 380 VDC. To further maintain the efficiency of power converters attached to this high voltage bus, it is necessary to limit the high voltage variations, e.g., to five percent.
In case of energy supply interruptions, it is common to have local diesel generators to provide the energy to the data center. However, such large scale diesel generators require up to several minutes to start and provide full power. This start-up transition time must be bridged by batteries or other short term energy supply components (e.g., capacitors or fly wheels). Depending on where and how such local short term energy sources are being attached, large voltage deviations on the high voltage DC bus may result.
It is therefore required to have a DC/DC converter which operates at very high efficiency when the high voltage DC bus is within a tight regulation band, but also can sustain large voltage variations during transition periods over several tens of seconds to a few minutes without losing regulation on its output. Such a converter will allow the back-up batteries to attach directly to the high voltage DC bus used to transition from normal grid operation to diesel generators.
FIG. 1 shows a typical DC/DC converter 100 with an input filter 101 (including in the illustrated example a capacitor C1, inductor L1, and capacitor C3) and a discharge resistor R1 to discharge the filter capacitors C1/C3 when the converter 100 is unplugged from an input power source Vi. The filter 101 is followed by a booster stage 102 (including in the illustrated example an inductor L2, switch S0, and diode D2) which is bypassed by diode D1 if the input voltage is higher than the maximum booster operating voltage. The booster stage 102 is followed by an energy storage and filter capacitor C2 and a DC/DC stage 103 providing galvanic isolation and a low voltage output.
The converter 100 of FIG. 1 suffers from several deficiencies: (a) the discharge resistor R1 creates permanent energy losses; (b) the booster stage has low efficiency because of the diode rectification; (c) when the booster stage is off, it is bypassed by diode D1, but this diode also generates significant losses; and (d) when the booster stage is off, several components are not in use (e.g., switch S0, diode D2, inductor L2) and poor power density of the overall converter will result.